package lily.phs.child;  

import android.content.Context;  
import android.util.AttributeSet;  
import android.util.Log;  
import android.view.MotionEvent;  
import android.view.VelocityTracker;  
import android.view.View;  
import android.view.ViewConfiguration;  
import android.view.ViewGroup;  
import android.widget.Scroller;  
/** 
 * 仿Launcher中的WorkSapce，可以左右滑动切换屏幕的类 
 * @author Yao.GUET 
 * blog: http://blog.csdn.net/Yao_GUET 
 * date: 2011-05-04 
 */  
public class ScrollLayout extends ViewGroup {  
    private static final String TAG = "ScrollLayout";  
    private Scroller mScroller;  
    private VelocityTracker mVelocityTracker;  
      
    private int mCurScreen;  
    private int mDefaultScreen = 0;  
      
    private static final int TOUCH_STATE_REST = 0;  
    private static final int TOUCH_STATE_SCROLLING = 1;  
      
    private static final int SNAP_VELOCITY = 600;  
      
    private int mTouchState = TOUCH_STATE_REST;  
    private int mTouchSlop;  
    private float mLastMotionX;  
    private float mLastMotionY;  
    public ScrollLayout(Context context, AttributeSet attrs) {  
        this(context, attrs, 0);  
        // TODO Auto-generated constructor stub  
    }  
    public ScrollLayout(Context context, AttributeSet attrs, int defStyle) {  
        super(context, attrs, defStyle);  
        // TODO Auto-generated constructor stub  
        mScroller = new Scroller(context);  
          
        mCurScreen = mDefaultScreen;  
        mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();  
    }  
    @Override  
    protected void onLayout(boolean changed, int l, int t, int r, int b) {  
        // TODO Auto-generated method stub  
        int childLeft = 0;  
        final int childCount = getChildCount();  
          
        for (int i=0; i<childCount; i++) {  
            final View childView = getChildAt(i);  
            if (childView.getVisibility() != View.GONE) {  
                final int childWidth = childView.getMeasuredWidth();  
                childView.layout(childLeft, 0,   
                        childLeft+childWidth, childView.getMeasuredHeight());  
                childLeft += childWidth;  
            }  
        }  
    }  
    @Override    
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {     
        Log.e(TAG, "onMeasure");  
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);     
    
        final int width = MeasureSpec.getSize(widthMeasureSpec);     
        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);     
        if (widthMode != MeasureSpec.EXACTLY) {     
            throw new IllegalStateException("ScrollLayout only canmCurScreen run at EXACTLY mode!");   
        }     
    
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);     
        if (heightMode != MeasureSpec.EXACTLY) {     
            throw new IllegalStateException("ScrollLayout only can run at EXACTLY mode!");  
        }     
    
        // The children are given the same width and height as the scrollLayout     
        final int count = getChildCount();     
        for (int i = 0; i < count; i++) {     
            getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);     
        }     
        // Log.e(TAG, "moving to screen "+mCurScreen);     
        scrollTo(mCurScreen * width, 0);           
    }    
      
    /** 
     * According to the position of current layout 
     * scroll to the destination page. 
     */  
    public void snapToDestination() {  
        final int screenWidth = getWidth();  
        final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;  
        snapToScreen(destScreen);  
    }  
      
    public void snapToScreen(int whichScreen) {  
        // get the valid layout page  
        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));  
        if (getScrollX() != (whichScreen*getWidth())) {  
              
            final int delta = whichScreen*getWidth()-getScrollX();  
            mScroller.startScroll(getScrollX(), 0,   
                    delta, 0, Math.abs(delta)*2);  
            mCurScreen = whichScreen;  
            invalidate();       // Redraw the layout  
        }  
    }  
      
    /**
     * 转到指定的页数
     * @param whichScreen 页数，首页为0
     */
    public void setToScreen(int whichScreen) {  
        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));  
        mCurScreen = whichScreen;  
        scrollTo(whichScreen*getWidth(), 0);  
    }  
      
    public int getCurScreen() {  
        return mCurScreen;  
    }  
      
    @Override  
    public void computeScroll() {  
        // TODO Auto-generated method stub  
        if (mScroller.computeScrollOffset()) {  
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());  
            postInvalidate();  
        }  
    }  
    @Override  
    public boolean onTouchEvent(MotionEvent event) {  
        // TODO Auto-generated method stub  
          
        if (mVelocityTracker == null) {  
            mVelocityTracker = VelocityTracker.obtain();  
        }  
        mVelocityTracker.addMovement(event);  
          
        final int action = event.getAction();  
        final float x = event.getX();  
        final float y = event.getY();  
          
        switch (action) {  
        case MotionEvent.ACTION_DOWN:  
            Log.e(TAG, "event down!");  
            if (!mScroller.isFinished()){  
                mScroller.abortAnimation();  
            }  
            mLastMotionX = x;  
            break;  
              
        case MotionEvent.ACTION_MOVE:  
            int deltaX = (int)(mLastMotionX - x);  
            mLastMotionX = x;  
              
            scrollBy(deltaX, 0);  
            break;  
              
        case MotionEvent.ACTION_UP:  
            Log.e(TAG, "event : up");     
            // if (mTouchState == TOUCH_STATE_SCROLLING) {     
            final VelocityTracker velocityTracker = mVelocityTracker;     
            velocityTracker.computeCurrentVelocity(1000);     
            int velocityX = (int) velocityTracker.getXVelocity();     
            Log.e(TAG, "velocityX:"+velocityX);   
              
            if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {     
                // Fling enough to move left     
                Log.e(TAG, "snap left");  
                snapToScreen(mCurScreen - 1);     
            } else if (velocityX < -SNAP_VELOCITY     
                    && mCurScreen < getChildCount() - 1) {     
                // Fling enough to move right     
                Log.e(TAG, "snap right");  
                snapToScreen(mCurScreen + 1);     
            } else {     
                snapToDestination();     
            }     
            if (mVelocityTracker != null) {     
                mVelocityTracker.recycle();     
                mVelocityTracker = null;     
            }     
            // }     
            mTouchState = TOUCH_STATE_REST;     
            break;  
        case MotionEvent.ACTION_CANCEL:  
            mTouchState = TOUCH_STATE_REST;  
            break;  
        }  
          
        return true;  
    }  
    @Override  
    public boolean onInterceptTouchEvent(MotionEvent ev) {  
        // TODO Auto-generated method stub  
        Log.e(TAG, "onInterceptTouchEvent-slop:"+mTouchSlop);  
          
        final int action = ev.getAction();  
        if ((action == MotionEvent.ACTION_MOVE) &&   
                (mTouchState != TOUCH_STATE_REST)) {  
            return true;  
        }  
          
        final float x = ev.getX();  
        final float y = ev.getY();  
          
        switch (action) {  
        case MotionEvent.ACTION_MOVE:  
            final int xDiff = (int)Math.abs(mLastMotionX-x);  
            if (xDiff>mTouchSlop) {  
                mTouchState = TOUCH_STATE_SCROLLING;  
                  
            }  
            break;  
              
        case MotionEvent.ACTION_DOWN:  
            mLastMotionX = x;  
            mLastMotionY = y;  
            mTouchState = mScroller.isFinished()? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;  
            break;  
              
        case MotionEvent.ACTION_CANCEL:  
        case MotionEvent.ACTION_UP:  
            mTouchState = TOUCH_STATE_REST;  
            break;  
        }  
          
        return mTouchState != TOUCH_STATE_REST;  
    }  
      
}  